Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, CO, 80401, USA.
Biology Department, Southern California Coastal Water Research Project, Costa Mesa, CA, 92626, USA.
J Environ Manage. 2021 Jul 1;289:112560. doi: 10.1016/j.jenvman.2021.112560. Epub 2021 Apr 12.
Managing river temperature in highly urbanized stream systems is critical for maintaining aquatic ecosystems and associated beneficial uses. In this work, we updated and utilized a mechanistic river temperature model, i-Tree Cool River, to evaluate the cooling impacts of two ecological restoration scenarios: (1) an alternative streambed material limecrete and (2) shading effects of tree planting in riparian areas. The i-Tree Cool River model was modified to account for diurnal fluctuations of streambed temperature, which is relevant in shallow urban streams where lack of natural shading combined with low heat capacity of the water column can make diurnal fluctuations relatively extreme. The model was calibrated and validated on a 4.2 km reach of Compton Creek in the Los Angeles River watershed, California. Two native fish, arroyo chub (Gila orcuttii) and unarmored threespine stickleback (Gasterosteus aculeatus williamsoni), were considered the target species for assessing thermal habitat suitability. Key findings include: (1) model performance was improved when accounting for diurnal fluctuations in bed temperature (R increased from 0.43 to 0.68); and (2) substrate rehabilitation and tree planting can potentially reduce summertime temperatures to within the documented spawning temperature thresholds for the focal fish species. Using limecrete as an alternative material for the concrete bottom decreased the median river temperature metrics: maximum weekly maximum, maximum weekly average, and minimum weekly minimum temperatures by an average of 3 °C (13%) to 20.4 °C, 19.7 °C, and 17.8 °C, respectively. Tree planting in the riparian corridor decreased the average river temperature metrics by an average of 0.9 °C (4%) to 22.7 °C, 22 °C, and 19 °C, respectively. Combining the two scenarios decreased the river temperature metrics by an average of 4 °C (18%) to 18.2 °C. Therefore, water temperature would not be a limiting factor in potential reintroduction of the focal fish species to Compton Creek if restoration were implemented. Implications of this work could be used by urban forest and water managers for restoring thermally polluted rivers in other urban areas.
管理高度城市化河流系统的水温对于维持水生生态系统和相关的有益用途至关重要。在这项工作中，我们更新并利用了一种机制河流温度模型，i-Tree Cool River，来评估两种生态恢复情景的冷却影响：（1）替代河床材料石灰凝土和（2）河岸地区植树的遮荫效果。i-Tree Cool River 模型进行了修改，以考虑河床温度的昼夜波动，这在浅城市溪流中很重要，在这些溪流中，由于缺乏自然遮荫和水柱的低热容量，昼夜波动可能相对极端。该模型在加利福尼亚州洛杉矶河流域的康普顿溪 4.2 公里长的河段进行了校准和验证。两种本地鱼类，峡谷鲦鱼（Gila orcuttii）和无甲三刺鱼（Gasterosteus aculeatus williamsoni）被认为是评估热生境适宜性的目标物种。主要发现包括：（1）考虑到河床温度的昼夜波动，模型性能得到了提高（R 值从 0.43 提高到 0.68）；（2）基质修复和植树造林有可能将夏季温度降低到记录的焦点鱼类物种的产卵温度阈值内。使用石灰凝土作为混凝土底部的替代材料，将中值河流温度指标：每周最高温度、每周最高平均温度和每周最低平均温度分别降低了 3°C（13%）至 20.4°C、19.7°C 和 17.8°C。河岸带植树造林将平均河流温度指标降低了 0.9°C（4%）至 22.7°C、22°C 和 19°C。将这两种情况结合起来，将河流温度指标平均降低了 4°C（18%）至 18.2°C。因此，如果实施恢复，水温不会成为将焦点鱼类重新引入康普顿溪的限制因素。这项工作的意义可以为城市森林和水资源管理者在其他城市地区恢复受热力污染的河流提供参考。
